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Multi-Dimensional Damage Detection for Surfaces and Structures

Monday, 01 July 2013

This system determines the size, depth, and location of damage in a multi-layered system.

Current designs for inflatable or semirigidized
structures for habitats and space
applications use a multiple-layer construction,
alternating thin layers with
thicker, stronger layers, which produces a
layered composite structure that is much
better at resisting damage. Even though
such composite structures or layered systems
are robust, they can still be susceptible
to penetration damage.

The ability to detect damage to surfaces
of inflatable or semi-rigid habitat
structures is of great interest to NASA.
Damage caused by impacts of foreign
objects such as micrometeorites can rupture
the shell of these structures, causing
loss of critical hardware and/or the life of
the crew. While not all impacts will have a
catastrophic result, it will be very important
to identify and locate areas of the
exterior shell that have been damaged by
impacts so that repairs (or other provisions)
can be made to reduce the probability
of shell wall rupture. This disclosure
describes a system that will provide realtime
data regarding the health of the
inflatable shell or rigidized structures,
and information related to the location
and depth of impact damage.

The innovation described here is a
method of determining the size, location,
and direction of damage in a multi-layered
structure. In the multi-dimensional
damage detection system, layers of two-dimensional
thin film detection layers are
used to form a layered composite, with
non-detection layers separating the detection
layers. The non-detection layers may
be either thicker or thinner than the
detection layers. The thin-film damage
detection layers are thin films of materials
with a conductive grid or striped pattern.
The conductive pattern may be applied by
several methods, including printing, plating,
sputtering, photolithography, and
etching, and can include as many detection
layers that are necessary for the structure
construction or to afford the detection
detail level required. The damage is
detected using a detector or sensory system,
which may include a time domain
reflectometer, resistivity monitoring hardware,
or other resistance-based systems.

To begin, a layered composite consisting
of thin-film damage detection layers
separated by non-damage detection layers
is fabricated. The damage detection
layers are attached to a detector that provides
details regarding the physical health
of each detection layer individually. If damage
occurs to any of the detection layers, a
change in the electrical properties of the
detection layers damaged occurs, and a
response is generated. Real-time analysis
of these responses will provide details
regarding the depth, location, and size estimation
of the damage. Multiple damages
can be detected, and the extent (depth) of the damage can be used to generate prognostic information related
to the expected lifetime of the layered composite system.

The detection system can be fabricated very easily using off-the-
shelf equipment, and the detection algorithms can be written
and updated (as needed) to provide the level of detail needed
based on the system being monitored. Connecting to the thin
film detection layers is very easy as well. The truly unique feature
of the system is its flexibility; the system can be designed to gather
as much (or as little) information as the end user feels necessary.
Individual detection layers can be turned on or off as necessary,
and algorithms can be used to optimize performance. The
system can be used to generate both diagnostic and prognostic
information related to the health of layer composite structures,
which will be essential if such systems are utilized for space exploration.
The technology is also applicable to other in-situ health
monitoring systems for structure integrity.

This work was done by Martha Williams, Mark Lewis, and Luke
Roberson of Kennedy Space Center; and Pedro Medelius, Tracy Gibson,
Steven Parks, and Sarah Snyder of ASRC Aerospace Corporation. For
further information, contact the KSC Technology Transfer Office at
(321) 867-5033. KSC-13588

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